Sound recording



K. scHwARz SOUND RECORDING Nov. 5, 1940.

Filed Dec. 29, 1937 Snventor dzaar'z Gttomeg Patented Nov. 5 1940 UNITEDSTATES,

2,220,461 SOUND naconnmc Karl Schwarz, Berlin, Germany, assignor toKlangfllm G. m. b. E, Berlin, Germany, a corporation of GermanyApplication IClaim.

This invention relates* to the photographic recording of light impulsessuch as those of audio frequency, and has for its principal object theprovision of an improved apparatus and method 5 of operation wherebyblurring of such a record due to stray light is minimized or avoided.

It is known that photographic recording with ultra-violet light, forexample, has certain advantages. It is also found that such recordinghas certain disadvantages due to the strong stray light frequentlyencountered in the use of an ultra-violet camera. According to theinvention, there is provided an improved arrangement by which straylight is prevented from reaching the film. In this way, it is ensuredthat the sound record does not become blurred or hazy. More particularlythere has been provided a series of diaphragms which keep. the straylight from the object lens, but allow the useful light to pass.

0 These diaphragms may be located at any suitable point in the opticalsystem;

According to one modification of the invention,

a diaphragm oi a definite shape and size is arranged in front of theobject lens which' images 5 the light slit on the film. With thisarrangement, the swinging galvanometer mirror is imaged on the objectlens. In this case, it is advisable to give the diaphragm the shape ofthis image. with rectangular mirrors, the diaphragm 0 has also a.similar rectangular hole. With such a diaphragm, the stray light whichis reflected by' omitted, this reflected light would get into the objectlens and, consequently, on the film, thus making the record blurred.

The invention will be better understood from 5 the following descriptionwhen considered in connection with the accompanying drawing and itsscope is indicated by the appended claim.

Referring to the drawing I the invention, and

December 29, 1937, Serial No. 182,173 In Germany March'15, 1937 Figure 2is an explanatory diagram relating. to the operation of the arrangementof Fig. 1.

In the arrangement of Fig. 1, the light beam'is applied in the directionof the arrow to the swinging concave galva'nometer minor l0 and isreflected thence to the slit [2 by a prism II. A lens |2a images themirror III on the object lens l3 which images the slit l2 on film II. Aseries of diaphragms l5, l6, l1, l8 and I9 are arranged between objectlens l3 and slot I 2. These diaphragm transmit only that part of thelight which is absolutely required forethe recording. It will beobserved that the openings of the diaphragms become smaller fromdiaphragm l5 to diaphragm l9. This reductionin the size of the openingsdependson the aperture of the object lens and on the'slot dimensions. Itwill be apparent that the stray light originating anywhere in the camerais kept away from object lens I3 by the series of diaphragms l5l9. Inaddition, with the arrangement of Fig. 1, a diaphragm 20 which isseparately illustrated in Fig.2 may also phragm has a rectangularopening which is designed in such a size that exactly the rectangularmirror l0 which is designed in this case as a con cave mirror is imagedin the rectangular opening 'by lens l2a. In this way, any light which isreflected eventually outside of mirror l0, either by the holding handsof the mirror or by the enamel layer 'which is also reflected somewhatwith ultra-violet light, is kept away from the object lens.Consequently, a record which is free from stray light is obtained. Inthis way, the record is rendered more sharp and blurring of its edges isavoided.

I claim as my invention: e

A light impulse recorder'including means pro-' viding a light slit, areflector vibratable in accordance with said impulses for applying saidlight to a record surface, means for producing an image oi saidreflector at said lens, diaphragm means adjacent to said lens forconfining the illuminated area of said lens to said reflector image, and

be associated with object lens l3. This dia-' said slit, an objectivelens for said slit on means including a plurality of coaxial variablyaperture'd diaphragms tor excluding stray light from said lens.

